Timing is timing, so even if your distributor was off a tooth, your timing light is supposedly still telling you what the timing is. So a 20 degree advance is still a 20 degree advance no matter what.
What vacuum port are you reading off of? Ported or full? Has to be full or you won't get much of a reading until your throttle blades come off of idle.
Your engine shouldn't even run at 3" of vacuum. Well, it might run but just barely. You'd definitely be seeing some strange backfire issues and rough idle and bouncing needles and all the usual suspects I would suspect.
Check your vacuum source first.
But an engine that has been sitting for extended periods can develop piston ring issues. Only extended driving will determine if that's going to fix itself, or if a new ring-job is in your future. Luckily they fix themselves with driving more often than not. Or used to anyway...
Also I don't see where you mentioned where you're getting power to the Pertronix. It has to have full 12v to run consistently. If you're using the old Red w/green resistor wire it's not going to work. Some here have been lucky in using that wire, while many others have not. Check that.
And for timing, I would not necessarily trust the timing marks on ANY rebuilt Ford engine. In their infinite wisdom, they had three or four different versions of the timing marks on the damper rings, for different applications. If your damper is from a car, and your timing pointer for a truck, and neither for a Bronco, then your timing marks are completely useless and you simply have to time it by ear for now.
Only verifying TDC physically, then marking the damper ring or using timing tape to match the pointer on the particular engine will give you the ability to use the timing marks in the future.
Anyway, let us know what you find with the vacuum, and see if any of those other things are causing you trouble.
Paul
